1. Field of the Invention
This invention relates to a method of and system for processing a radiation image and more particularly to a method of and system for processing a radiation image which is taken using an irradiation field stop.
2. Description of the Related Art
It has been put into practice to photoelectrically read out a radiation image recorded on a radiograph film thereby obtaining an image signal representing the radiation image, carry out an adequate image processing on the image signal and output the processed image signal to a CRT, a laser printer or the like. Further there has been known a radiation image recording and reproducing system in which a medical radiation image such as of a human body is stored on a stimulable phosphor sheet, the stimulable phosphor sheet is then exposed to stimulating rays such as a laser beam which cause the stimulable phosphor sheet to emit light in proportion to the stored radiation energy, the light emitted from the stimulable phosphor sheet is photoelectrically detected and converted to an electric image signal, and the radiation image of the object is reproduced as a visible image on the basis of the electric image signal.
In such a radiation image recording and reproducing system, the recording system, read-out system, image processing system, CRT, laser printer and the like are not always installed in one location in a hospital but are often in separate locations and connected with each other by a network. Further, an image signal representing a radiation image recorded in a big hospital is sometimes transferred to a remote hospital without a large equipment such as a recording system through a network and a visible image is reproduced on a CRT in the hospital for diagnosis.
In order to minimize the irradiation dose to the object, a radiation image is sometimes recorded using an irradiation field stop so that only a necessary portion of the object is exposed to the radiation. The image signal representing a radiation image taken using an irradiation field stop is sometimes subjected to an image processing so that the image in the irradiation field becomes more suitable for diagnosis. See, for instance, Japanese Unexamined Patent Publication No. 3(1991)-98174. For example, when a radiation image taken using an irradiation field stop is reproduced on a CRT as it is, the area outside the irradiation field is reproduced at a high brightness on the CRT, which makes it hard to see the image. Accordingly the image signal is sometimes subjected to an image processing for lowering the brightness of the area outside the irradiation field. This processing is equivalent to a processing for increasing the density of the area outside the irradiation field in film output. (Such processings will be referred to as xe2x80x9coff-field darkening processingxe2x80x9d, hereinbelow.)
When transferring an image signal to a CRT or the like through a network, necessary image processings are generally carried out on the image signal before transfer in order to lighten the load on the system to which the image signal is to be transferred and the network, so that only the smallest necessary image signal, that is, the processed image signal is transmitted. It is true also for the image processing for making the area in the irradiation field to easy to see. That is, an irradiation field recognition processing is first carried out on an original image signal, thereby obtaining irradiation field information for distinguishing the area inside the irradiation field from the area outside the same (information representing the irradiation field or information representing the edge of the irradiation field, i.e., the boundary between the area inside the irradiation field and the area outside the irradiation field), for instance, an off-field darkening processing is carried out on the original image signal on the basis of the irradiation field information, and then the processed image signal is transferred to the output system such as a CRT, a laser printer or the like through a network.
Generally in the image processing system using a network, when the receiver side cannot obtain a normal image signal due to abnormality on the transmitter side, the transmitter side tries again the step where the abnormality occurred and transmits again the normal image signal.
However in the case where abnormality occurs in a processing for recognizing an irradiation field (e.g., an automatic prospective irradiation field recognition processing) and a part of the image is made invisible due to the abnormality, e.g., darkened though the image signal itself is normal, it is sometimes preferred that the image be made visible at once by cancelling the processing, even if the image becomes somewhat difficult to view, rather than repeating the processing taking a long time.
Further, there is a case where it is preferred that the irradiation field be corrected on the receiver side and the image processing be carried out on the basis of the corrected irradiation field.
In view of the foregoing observations and description, the primary object of the present invention is to provide a method of and a system for processing a radiation image in which an image output on the receiver side with an area considered to be outside a prospective irradiation field can be processed in a predetermined way and changed with the prospective irradiation field or cancelled with the processing in a short time.
In accordance with the present invention, an irradiation field recognition processing for recognizing a prospective irradiation field which is considered to be an irradiation field of a radiation image is carried out in an image information obtaining section, which is an image signal transmitter, and the information on the prospective irradiation field is transferred to an image output section, which is an image signal receiver, attached to a radiation image signal representing the radiation image or separately therefrom, and the image processing is carried out on the basis of the transferred information on the prospective irradiation field in the image output section.
That is, in accordance with a first aspect of the present invention, there is provided a method of processing a radiation image comprising the steps of
obtaining an image signal representing a radiation image and a prospective irradiation field information representing a prospective irradiation field of the radiation image,
transferring the prospective irradiation field information attached to the radiation image signal or separately therefrom to an image output section,
carrying out an image processing to make the image in the prospective irradiation field more suitable for viewing on the transferred image signal in the image output section on the basis of the prospective irradiation field information transferred, and
outputting a radiation image on the basis of the processed image signal.
The prospective irradiation field information may be obtained by various methods. For example, the prospective irradiation field information may be obtained by carrying out an automatic recognition processing on the image signal according to a predetermined algorithm as disclosed in U.S. Pat. Nos. 4,967,079 and 5,068,907 and and the like, or may be obtained by the operator designating a prospective irradiation field using an input means such as a mouse, a touch pen or the like viewing a radiation image displayed on a monitor.
As a method of automatically detecting a prospective irradiation field by carrying out a processing according to a predetermined algorithm, various known irradiation field recognition processings may be applied. For example, a dynamic contour extraction processing using Snakes algorithm may be employed as well as a processing in which prospective edge points are detected on the basis of differences between image signal components and a prospective edge is detected on the basis of the prospective edge points.
The term xe2x80x9cprospective irradiation fieldxe2x80x9d means an area which is considered to be an irradiation field in the recognition processing. That is, depending on the accuracy of the processing or input accuracy of the operator, the detected irradiation field cannot always precisely coincide with the real irradiation field existing in the radiation image (including a case where no irradiation field exists in the radiation image). Accordingly, in this specification, an area recognized as an irradiation field is referred to as xe2x80x9cprospective irradiation fieldxe2x80x9d in order to distinguish from the real irradiation field.
The expression xe2x80x9ctransferring the prospective irradiation field information attached to the radiation image signalxe2x80x9d means, for instance, determining a data format including the radiation image signal and the prospective irradiation field information and preparing and transferring the transferred data according to the data format, or transferring the prospective irradiation field information incorporated in header information. Otherwise the prospective irradiation field information may be incorporated in the radiation image signal as a part thereof and the radiation image signal and the prospective irradiation field information may be transferred as one radiation image signal. For example, the prospective irradiation field information may be incorporated in the image signal by allotting some lines of data of the image signal for storing the prospective irradiation field information. In this case, when two lines, 2000 picture elements (8 bits/picture element), are allotted for storing the prospective irradiation field information, a storage area of 4000 bytes can be ensured. Parameters representing the prospective irradiation field information can be stored in the storage area. In this case, though the last two lines of the image signal become not effective, such an ineffectiveness at an edge of the image gives rise to no problem in diagnosis.
Other various methods employed in data transfer can be employed in xe2x80x9ctransferring the prospective irradiation field information attached to the radiation image signalxe2x80x9d.
The image processing to make the image in the prospective irradiation field more suitable for viewing may be xe2x80x9coff-field darkening processingxe2x80x9d described above, that is, an image processing for lowering the brightness of the area outside the irradiation field when a visible image is displayed, for instance, on a CRT, or an image processing for increasing the density of the area outside the irradiation field when a visible image is recorded on film. Further the image processing may be an image processing for cutting or shading off the area outside the irradiation field.
According to whether the output radiation image is acceptable, the prospective irradiation field information may be corrected on the receiver side if necessary, i.e., if the output radiation image is not acceptable. When the prospective irradiation field information is corrected, an image processing to make the image in the prospective irradiation field more suitable for viewing may be carried out on the transferred image signal on the basis of the corrected irradiation field information, and when the prospective irradiation field information is not corrected, an image processing to make the image in the prospective irradiation field more suitable for viewing may be carried out on the transferred image signal on the basis of the transferred prospective irradiation field information. Then a visible image is output on the basis of the processed image signal.
An operator, doctor or the like on the receiver side views the radiation image output on the basis of the image signal processed on the basis of the prospective irradiation field information as transferred and determines whether the output radiation image is acceptable, that is, whether the prospective irradiation field information as transferred designates a proper area. When it is determined that the prospective irradiation field information as transferred designates an improper area, the prospective irradiation field information is corrected and otherwise need not be corrected.
To correct the prospective irradiation field information means to change the size, shape, number and the like of the prospective irradiation field(s). For example, when correction information that the prospective irradiation field should be of a rectangle (circle, ellipsoid or the like) and the number of the irradiation fields should be 0 (1, 2, 4 . . . ) is given by the receiver side, the prospective irradiation field information is corrected on the transmitter side or the receiver side according to an algorithm suitable for a predetermined correction conforming to the correction information and the corrected prospective irradiation field is output on the receiver side. In this case, to input the correction information representing that the number of the irradiation field is 0 and correct the prospective irradiation field information according to the correction information is to take it that there exists no irradiation field and process the whole image signal without carrying out an image processing on the basis of the irradiation field. Accordingly, in such a case, instruction for stopping the image processing on the basis of the prospective irradiation field may be directly input in place of the correction information representing that the number of the irradiation field is 0.
Operators designating a prospective irradiation field using an input means such as a mouse, a touch pen or the like viewing a radiation image displayed on a monitor should also be considered to be an operation of giving the correction information.
In accordance with a second aspect of the present invention there is provided a system for processing a radiation image which processes a radiation image according to the method of the first aspect. That is, the system of the second aspect comprises
an image information obtaining section which obtains an image signal representing a radiation image and a prospective irradiation field information representing a prospective irradiation field of the radiation image,
an image output section which comprises an image processing means which carries out an image processing to make an image in the prospective irradiation field more suitable for viewing on the transferred image signal on the basis of the prospective irradiation field information transferred and an image output means which outputs a radiation image on the basis of the processed image signal and
a transfer means which transfers the prospective irradiation field information attached to the radiation image signal or separately therefrom to the image output section from the image information obtaining section.
As the image output means, an image display means such as a CRT, an image recording means such as a laser printer which records an image on a photosensitive recording medium, and the like can be employed.
Each or one of the image information obtaining section and the image output section may have a correction means for correcting the prospective irradiation field information according to a predetermined correction information and the image output section may be further provided with a correction information input means which receives a predetermined correction information and outputs it to the corrections means so that the image processing means carries out the image processing, to make the image in the prospective irradiation field more suitable for viewing, on the transferred image signal on the basis of the corrected prospective irradiation field information when the prospective irradiation field information is corrected and on the basis of the transferred prospective irradiation field information when the prospective irradiation field information is not corrected.
In the method of and the system for processing a radiation image of the first and second aspects of the present invention, a radiation image is output on the receiver side on the basis of an image signal which has been processed on the basis of the prospective irradiation field information. In contrast, in the method of and the system for processing a radiation image of third and fourth aspects of the present invention, the radiation image is output on the basis of an image signal simply synthesized with a prospective irradiation field information and the image processing is carried out after the prospective irradiation field information is corrected according to the result of the synthesis.
That is, in accordance with the third aspect of the present invention, there is provided a method of processing a radiation image comprising the steps of
obtaining an image signal representing a radiation image and a prospective irradiation field information representing a prospective irradiation field of the radiation image,
transferring the prospective irradiation field information attached to the radiation image signal or separately therefrom to an image output section, and
synthesizing the transferred image signal with the transferred prospective irradiation field information and outputting a radiation image on the basis of the image signal synthesized with the prospective irradiation field information in the output section.
That is, since an image in which a line pattern representing the prospective irradiation field overlaps the radiation image is output, the arrangement, shape, number and the like of the prospective irradiation field(s) can be clearly judged.
Then the prospective irradiation field information may be corrected on the receiver side according to the judgment. When the prospective irradiation field information is corrected, an image processing to make the image in the prospective irradiation field more suitable for viewing may be carried out on the transferred image signal on the basis of the corrected irradiation field information, and when the prospective irradiation field information is not corrected, an image processing to make the image in the prospective irradiation field more suitable for viewing may be carried out on the transferred image signal on the basis of the transferred prospective irradiation field information.
In accordance with the fourth aspect of the present invention there is provided a system for processing a radiation image which processes a radiation image according to the method of the third aspect. That is, the system of the fourth aspect comprises
an image information obtaining section which obtains an image signal representing a radiation image and a prospective irradiation field information representing a prospective irradiation field of the radiation image,
an image output section which comprises an image processing means which synthesizes the image signal with the prospective irradiation field information and an image output means which outputs a radiation image on the basis of the image signal synthesized with the prospective irradiation field information and
a transfer means which transfers the prospective irradiation field information attached to the radiation image signal or separately therefrom to the image output section from the image information obtaining section.
Each or one of the image information obtaining section and the image output section may have a correction means for correcting the prospective irradiation field information according to a predetermined correction information and the image output section may be further provided with a correction information input means which receives a predetermined correction information and outputs it to the corrections means so that the image processing means carries out the image processing, to make the image in the prospective irradiation field more suitable for viewing, on the transferred image signal on the basis of the corrected prospective irradiation field information when the prospective irradiation field information is corrected and on the basis of the transferred prospective irradiation field information when the prospective irradiation field information is not corrected.
In accordance with the present invention, the prospective irradiation field information is transferred to the output side (the receiver side or the image output section) together with the image signal and the image processing to make the image in the prospective irradiation field more suitable for viewing is carried out on the output side. Accordingly the output side can hold the original image signal (the image signal before it is processed) and for instance, when the transferred prospective irradiation field information is not proper due to, for instance, improper irradiation field recognition processing carried out on the transmitter side (the image information obtaining side), the receiver side can quickly output a radiation image on the basis of the original image signal.
When the prospective irradiation field information is incorporated in the radiation image signal as a part thereof, the amount of data to be transferred is kept equal to that when only the image signal is transferred. Further in the case of an image output section having function of image processing or image synthesis, the prospective irradiation field information in the transferred image signal is recognized and an image processing or image synthesis is carried out on the basis of the prospective irradiation field information. In the case of an image output section not having such function, the prospective irradiation field information in the transferred image signal is ignored and a radiation image is output on the basis of the transferred image signal bearing thereon the prospective irradiation field information. Accordingly, the present invention can be applied to existing system by changing only a part thereof, whereby the introduction cost can be suppressed.
In the method and system in accordance with the third and fourth aspects of the present invention, since an image in which a line pattern representing the prospective irradiation field overlaps the radiation image is output, the state of the prospective irradiation field (the arrangement, shape, number and the like of the prospective irradiation field(s)) in the entire radiation image can be viewed and accordingly whether the prospective irradiation field is proper can be more clearly judged.
Further in the systems and the methods in accordance with the present invention, when the prospective irradiation field information is corrected according to whether the output radiation image is acceptable, not only a radiation image can be output on the basis of the original image signal, that is, the image signal before the image processing or the image synthesis, but also a radiation image which is properly processed on the basis of the corrected prospective irradiation field information can be obtained in a short time on the receiver side.
Further when the aforesaid off-field darkening processing is employed as the image processing based on the prospective irradiation field information, the output image can be more suitable for diagnosis since the image in the irradiation field is not affected by the image outside the irradiation field.